1. Field of the Invention
The present invention relates to control devices for hydraulic cylinders, and relates to operating machines including the same.
2. Description of the Related Art
A control device that prevents damage to a hydraulic cylinder by controlling the drive of a piston when a stroke end is approached is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2004-293628.
In this device, it is determined whether the position of the piston is located in a predetermined stroke-end area on the basis of the pressure inside the hydraulic cylinder. When it is determined that the position is in the predetermined area, the piston is decelerated by regulating supply pressure and discharge pressure to the hydraulic cylinder.
However, this device starts uniformly decelerating the piston when the piston approaches a position a predetermined distance from the stroke end (stroke-end area). Therefore, when the speed of the piston that has reached this position is excessively high, a large force depending on the inertia is applied to the piston. As a result, the internal pressure of the cylinder (internal pressure of the discharge section) may be excessively increased so as to damage the cylinder.
In order to reliably prevent such damage, the deceleration may be started earlier by expanding the stroke-end area. However, in such cases, the deceleration timing is advanced even when the speed of the piston is not excessively high, resulting in reduced working efficiency.